Snap refresh over metered connections

[mborzecki]

@abeato

IMHO I think the right course of action would be to check also interfaces managed by networkd , sort of replicating NM’s logic in snapd. NM actually does not do anything too clever here (wwan -> guess it is metered, otherwise is not), but for bluetooth interfaces which are not supported by networkd anyway. So doing a simple check by using networkd interface type and merging that with NM’s value is feasible. This would have the advantage of making the feature available also when NM is not present.

We’ll need to discuss that. I’m not particularly fond of poking both.